1. Field
The present disclosure relates generally to communication, and more specifically to decoding a broadcast control channel in a wireless communication network.
2. Background
The 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) represents a major advance in cellular technology and is the next step forward in cellular 3G services as a natural evolution of the Global System for Mobile Communications (GSM) and Universal Mobile Telecommunications System (UMTS). LTE provides for an uplink speed of up to 50 megabits per second (Mbps) and a downlink speed of up to 100 Mbps and brings many technical benefits to cellular networks. LTE is designed to meet carrier needs for high-speed data and media transport as well as high-capacity voice support well into the next decade. Bandwidth is scalable from 1.25 MHz to 20 MHz. This suits the needs of different network operators that have different bandwidth allocations, and also allows operators to provide different services based on spectrum. LTE is also expected to improve spectral efficiency in 3G networks, allowing carriers to provide more data and voice services over a given bandwidth. LTE encompasses high-speed data, multimedia unicast and multimedia broadcast services.
The LTE physical layer (PHY) is a highly efficient means of conveying both data and control information between an enhanced base station (eNodeB) and mobile user equipment (UE). The LTE PHY employs some advanced technologies that are new to cellular applications. These include Orthogonal Frequency Division Multiplexing (OFDM) and Multiple Input Multiple Output (MIMO) data transmission. In addition, the LTE PHY uses Orthogonal Frequency Division Multiple Access (OFDMA) on the downlink (DL) and Single Carrier—Frequency Division Multiple Access (SC-FDMA) on the uplink (UL). OFDMA allows data to be directed to or from multiple users on a resource block basis for a specified number of symbol periods.
Recently, LTE Advanced is an evolving mobile communication standard for providing 4G services. Being defined as 3G technology, LTE does not meet the requirements for 4G, also called IMT Advanced as defined by the International Telecommunication Union, such as peak data rates up to 1 Gbit/s. Besides the peak data rate, LTE Advanced also targets faster switching between power states and improved performance at the cell edge.
To facilitate communication with remote terminals in a mobile networking arrangement, network base stations broadcast wireless signals that include synchronization and/or acquisition signals. The signals vary from one system to another (e.g., an LTE system can utilize a primary synchronization channel (PSC) and secondary synchronization channel (SSC), whereas an Ultra Mobile Broadband (UMB) system can utilize TDM1, TDM2, and TDM3 acquisition pilots), but typically include data that facilitates various functions pertinent to mobile communications. Examples of such functions include identifying a base station broadcasting a wireless signal and a type of system associated with the base station (e.g., LTE, UMB, etc.), providing initial timing and/or frequency data for demodulating the signal, conveying initial system parameters concerning the system (e.g., whether synchronous or asynchronous, what Time Division Duplex (TDD) partitioning is used), and so on. In addition, wireless signals comprise control channels that provide configuration information utilized by remote terminals to register on the mobile network and communicate with the network. Paging services, utilized to notify a terminal of an inbound call, are one example of functions performed with control channel information in some systems.
Control channel and pilot information are often provided in the dedicated resources (e.g., time, frequency) of a wireless signal. This provides an advantage in that receiving devices can reliably analyze predetermined resources to obtain demodulation and synchronization data concerning the wireless signal. One drawback, however, is that additional resources might not be available for other information pertinent to initial acquisition or signal synchronization. For instance, where a standard governing a mobile system provides specific resources for pilot and control information, the signal might have limited capacity to accommodate advancements in the network architecture after the standard is established. Thus, for instance, where a system evolves to have multiple acquisition/control states, transmission states, or the like, not envisioned by the standard, it can be difficult to convey system state information.
One particular problem is illustrated by blind decoding. When a mobile device first enters a macro network, system and/or channel information from the network may be necessary in order to communicate with the network. However, if the mobile device is not already acclimated with the network, some of the information might have to be decoded blindly, or without specific instruction on how to decode a channel or where system information exists within a received signal. One mechanism for blind decoding is to analyze the received signal according to multiple known states. Where a particular known state is well correlated with analyzed signals, it can be assumed that the particular state corresponds with the signal. However, this assumption can lead to false alarms, where multiple states sufficiently correlate to the analyzed signal. Multiple correlations can occur, for instance, where low signal to noise (SNR) is prevalent.
Recently, it has been recognized that communicating broadcast control information multiple times can increase the likelihood of successfully receiving the information. Instances where the transmission remains static, gain can be realized by combining the multiple transmissions before decoding. This approach has generally been referred to as Chase Combining In order to extend instances where such a gain can be realized, a linear channel coding approach has been described that addresses a variant portion of the transmission that increments by one between subsequent transmissions. To summarize, let i0 and i1 be first and second transmissions with the corresponding codewords being c0 and c1, where the linear channel coding can be represented as:c0=f(i0)c1=f(i1)If i1=i0+e,c1=f(i1)=f(i0+e)c1=f(i0)=f(e)c1=c0+f(e)If e is known, and hence f(e) is known, then c1 can be modified to an equivalent c0 codeword and decoded after combining with the first transmission.
In particular, this technique requires negating a predictable difference between transmissions before combining. Unfortunately, it is not always possible to accurately predict a difference between transmissions. A difference in channel coded transmissions can be one of a set of values that prevents realizing a combining gain.